The present invention relates to a safety device for igniting fuel gases or gaseous fuels discharged by a flare.
A large number of flare igniter types have already been proposed. They can be placed in two categories, one consisting of devices having a direct thermal action and the other of installations comprising a pilot burner which is itself ignited by a device of the aforementioned category.
In the case of ignition devices with a direct thermal action, the passage of an electric current is generally used to raise a solid body by the Joule effect or a gas volume is ignited by sparking between two electrodes to a temperature exceeding the ignition point of the gas discharged by the flare.
Conventional electrical resistors cannot be continually exposed to the flames of the flare where they would be subject to active abrasion and corrosion and would consequently undergo a very rapid deterioration. When such resistors are used, they are mounted on a mechanism that serves to remove them from the space occupied by the flame as soon as ignition has taken place.
The electrodes of the spark gaps are in turn sensitive to abrasion, corrosion or oxidation, as well as to deposits of carbon black and other solid waste resulting from incomplete combustion. In order to obviate the effects of abrasion and corrosion of electrodes, mechanisms have been designed for maintaining the spacing between the ends of the electrodes at the optimum sparking distance for the electric arc. However, despite these improvements, these mechanisms remain fragile under difficult operating conditions created by the atmosphere surrounding a flare orifice when the flare is operating.
U.S. Pat. No. 4,147,493 of STRAITZ III describes a device making it possible to displace a spark gap and its control means between an ignition position and a position removed from the area surrounding the flare orifice. This installation is complex and in the retracted position, if the flare is extinguished, safety is not completely ensured because to be effective the igniter must be brought into its ignition position close to the flare orifice and said operation cannot be instantaneous.
The various igniters based on a direct thermal action bring about an immediate ignition of the flare when there is a considerable gaseous emission. However, if the discharged volume is small compared with the optimum flow rate for which the flare was designed and as a function of the turbulence of the atmosphere, there can be a significant delay before effective ignition takes place, despite a large number of devices placed around the flare orifice.
Igniters with a pilot light are very widely used. Thus, it has been recognised that the ignition of a flare by means of a gas pilot burner is substantially guaranteed, being independent of the size of the gaseous emission and independent of the orientation and force of the wind and the atmospheric turbulence resulting therefrom.
Moreover, when the composition of the gases to be discharged and destroyed is such that very strict safety precautions must be taken, e.g. when there is a high H.sub.2 S content, it is indispensable to provide at least one permanent pilot light supplied with an auxiliary fuel gas.
In the case of large flares, at least two pilot lights are used having symmetrical axes with respect to the flare axis in the vertical plane of the prevailing wind. For even greater security and to take account of unforeseen circumstances, in general four pilot lights are fitted, two in the plane of the prevailing wind and two in the perpendicular plane.
U.S. Pat. No. 2,460,016 (KUHN), U.S. Pat. No. 2,869,631 (ZINK), U.S. Pat. No. 3,537,091 (SCHENKENBERG) and U.S. Pat. No. 3,816,059 (STRAITZ) describe such installations.
Supplying auxiliary fuel gas to two or four pilot lights constitutes a high daily expenditure, which has been hitherto accepted as the price of safety.